Articulators in Orthodontics

Chewing the facts: Part 1

Editor’s note: This is the first part of a two-part article. The conclusion will appear in the June issue.

The utility of articulators as a diagnostic aid in orthodontics is controversial and has been a heated debate for more than 3 decades. I have certainly been one of the most outspoken critics of the validity of articulators in orthodontics, having debated on several occasions the leading orthodontic gnathology proponent and guru of the day, the late Ronald Roth, DDS, MS. Parenthetically, I admired the passion Ron had for the subject of orthodontic gnathology.

For sure, everything I can write on this topic I have already clearly written and supported with well-thought-out arguments, science and evidence, and a plethora of references.^1-8 It is, therefore, impossible to present my nongnathologic orthodontic view as well in these few pages as I (and my coauthors) have done in the original work. So I encourage those not familiar with my (and my coauthors’) publications to read them.

Interestingly, most of the problems I have with the use of articulators in orthodontics come long before the articulator comes into play. That is, the title and wording of much of my writings use the word “articulator” because the culmination of the orthodontic gnathologic view ends with the mounting of dental casts on an articulator. However, I am critical of the entire orthodontic gnathologic philosophy and the unscientific tenets that are used to support this viewpoint (including the concept of centric relation).

The gnathologic view essentially focuses on the following: attaining canine-protected occlusion (mutually protected), establishing coincidence of maximum intercuspation (MI) of the teeth at the same time the condyles are seated in an anterior-superior centric relation (MI-CR), and the use of fully adjustable articulators.^1,2 And I should mention at the outset that there are several types of articulators: fully adjustable, semiadjustable, arcon, nonarcon, polycentric hinge, and so forth. I briefly dealt with the evaluation of the different types of articulators in a previous report¹; therefore, the present discussion is a general critique of the use of articulators in orthodontics.

As an aside, I will say that Michael C. Alpern, DDS, MS, does present a strong argument that the polycentric hinge articulator may have advantages over the others.⁹ I should also make it clear that there is not just one unified gnathologic view. The differences in views typically surround issues concerning the definition, recording, and measurement of centric relation (CR). For example, in general dentistry the Las Vegas Institute (LVI) has adopted the Jankelson “Myotronics” concept for recording the so-called neuromuscular CR position by the use of a myomonitor (similar to a TENS unit). It does appear, however, that the orthodontic gnathologic view is relatively united, and the most popular and vocal camp is that led by the late Roth. The purpose of this paper is to present the nongnathologic orthodontic viewpoint from my personal, iconoclastic perspective, which dates back more than 30 years. My goal in investigating gnathology in orthodontics has been a search for “truth.”

Graduate Studies

When I was an orthodontic graduate student in the mid 1970s at the University of Pittsburgh, my thesis study compared the functional occlusions of a group of subjects who had been treated orthodontically with that of an untreated group of subjects who naturally possessed an ideal static occlusion.^10-12 I was convinced at that time, based upon the gnathologic training I had gotten at dental school (we had a very intensive course and used fully adjustable Denar Articulators, with and without pantographs), as well as the writings and presentations of Roth, that there would be a difference in the functional occlusions between postorthodontically treated and untreated subjects. I conjectured that the functional occlusions of orthodontically treated subjects would possess balancing side occlusal interferences (which at the time was considered “bad”) and that the untreated group would possess this beautiful and perfect canine-protected occlusion. Parenthetically, it was believed at that time that orthodontists generally treated only to static occlusion goals and ignored function (that is, the principles of gnathology) and therefore were predisposing their patients to an iatrogenically produced balanced occlusion and eventual TMD (Temporomandibular Disorder).

To my surprise and chagrin, the findings of my thesis study demonstrated that both groups possessed balanced occlusion. Parenthetically, there is a difference between a balancing side contact and a balancing side interference. Contacts are benign, while occlusal interferences are “destructive” and require adjustment. This left me in quite a conundrum, and I began to rethink my view and support for the principles of gnathology. I started to research and investigate the issue of occlusion/TMD/orthodontics with renewed vigor. As I read more and more, I learned that the typical and natural functional occlusion type may not necessarily be canine-protected occlusion as I was taught. As Woda et al¹³ stated in a very comprehensive literature review published in the Journal of Prosthetic Dentistry in 1979, “pure canine protection or pure group function rarely exists and balancing contacts seem to be the general rule in the population of contemporary civilization.” Wow! This was eye-opening. It should be evident to the reader that I was originally a gnathologic believer turned atheist, or is it “agnathist”?

Several years later, another graduate student at Pitt carried out a second orthodontic/TMD research project that compared the TMD status of orthodontically treated subjects with untreated subjects (with about 100 patients in each group) and found again no difference.¹⁴ And then, the studies of Cyril Sadowsky, DDS, MS, and his coworkers¹⁵ appeared in the American Journal of Orthodontics in 1980 and 1984,¹⁶ which demonstrated a similar finding as our Pitt studies. First, the functional occlusions of orthodontically treated and untreated subjects are alike; for the most part, both groups possessed balanced occlusion and not canine-protected or group function. Second, Sadowsky et al^15,16 found that there was no difference in TMD signs and symptoms between the two groups. The modern and unequivocal evidence-based view is that orthodontic treatment does not cause TMD.^6,17,18

The Evolution of the Gnathologic View

This should have been a staggering blow for orthodontic gnathology. Recall, the orthodontic gnathologists ardently promulgated the view that because orthodontists were not practicing in a climate governed by gnathologic principles, they were creating TMD problems for their orthodontic patients. In the mid to late 1980s, Roth seemed to somewhat back off his argument that orthodontics caused TMD, but started to apply a new spin explaining why orthodontists should still continue to ascribe to the principles of gnathology. According to Roth, it was just not good enough for the profession of orthodontics to treat merely to do no harm to orthodontic patients’ existing TMJs. Orthodontists should be obliged to improve the TMJ status of their patients (now and in the future), and obviously this comes back again to applying the principles of gnathology.

In addition, the orthodontic gnathologists in the 1970s advocated and preached a view of CR that has now been debunked.² To wit, Roth supported a retruded CR position (posterior-superior position of the condyles) in the glenoid fossa in the 1970s, and then, sometime in the 1980s, recanted and switched his view to comply with the contemporary thinking of the day, which was an anterior-superior CR position. As you can recognize, this is a totally opposite viewpoint to the one he passionately supported in his early career. Roth did not simply change his view of CR a few nanometers or so, but from one end of the spectrum to the other—posterior-superior to anterior-superior! This should have been another embarrassment to the orthodontic gnathology camp and a warning to those orthodontists supporting and blindly following Roth. Of note: In the early years, Roth was most concerned with nongnathologists not properly recognizing and diagnosing sagittal CR discrepancies, then more recently recanted and said he was now more concerned with the problem of undiagnosed transverse and/or vertical CR discrepancies.¹⁹

Retruded Centric Relation

I never bought into the concept of retruded CR in the 1970s because I, as well as others, believed it to be an unnatural and unphysiologic position, and also contrary to the intraoral telemetry data of that day. (Telemetry technology invented for monitoring space flights was first used in dentistry in 1956. It involved the placement of miniature radio implants into crowns, onlays, and bridges, and then recording the radio frequencies outside the mouth with the purpose of evaluating tooth contacts.) When the entire dentitions of subjects were prosthetically rehabilitated and restored and evaluated by telemetry to retruded CR with interdigitated teeth in centric relation occlusion (CRO), subjects continued to function in centric occlusion (CO); approximately 2 mm anterior to CRO (and retruded CR).^20-22 Based on this research, it should have been evident that retruded CR was not a physiologic position. This information was apparently ignored by the gnathologists of that time.

In January 1983, the ADA published the first of its two conference reports on TMD.²³ The recommendations from this conference, as well as those of the second conference published in 1990²⁴ (and also the NIH conference in 1996²⁵), were detrimental to the occlusionist/gnathologic view. First, the concept of TMJ pain/dysfunction became temporomandibular disorders (TMD), and TMD was recognized as a collection of a half dozen or so subdisorders, each having its own multifactorial etiologies. Occlusal factors went from being primary etiologic agents to having a secondary and associational role. Centric slides present in some TMD subjects were argued to be the result of the TMD rather than the cause. Condyle position (or CR position of any kind) was not believed to be causally related to the development of TMD: The “normal” position of the condyles in the glenoid fossa is quite variable and involves a range of positions. Eccentricity of the condyles in the glenoid fossa was not considered diagnostic of TMD.^22,26 Robert Keim, DDS, EdD, editor of the Journal of Clinical Orthodontics, wrote, “The neuromuscular school tells us that there is a range of acceptable positions (centric) … If we clinicians continue to place emphasis on establishing ‘harmony’ between CO and some mythical concept of CR, we are doing ourselves a disservice.”²⁷ The information from the first ADA Conference on TMD²³ and the relevance to orthodontics was clearly disseminated to the profession; the first ADA TMD Conference Report was republished in the American Journal of Orthodontics in June 1983, and my brother Dan and I did a follow-up article explaining how the ADA TMD panel guidelines would affect orthodontics.²⁸

TMD on Trial

Then the infamous Michigan (Brimm v Malloy) TMD lawsuit took place in 1987. For those not familiar with the case, the bottom line is that a legal judgment was held against a defendant orthodontist—at the cost of approximately $1 million—for allegedly causing TMD in a 16-year-old female patient. The plaintiff patient possessed an Angle’s Class II (1) malocclusion that was treated with full fixed orthodontic appliances in combination with maxillary bicuspid extractions (no mandibular extractions). It was alleged that the defendant orthodontist precipitated a TMJ internal derangement in the patient from the over-retraction of her upper incisors against her lower incisor/mandible, resulting in distal displacement of her condyles. Once again, the debate about orthodontics causing TMD was reinvigorated. This time around, the mantra from a faction of the gnathology camp was not so much that occlusal disharmonies were the cause of TMD, but the cause of TMD was due to the incorrect position of the condyles. That is, distally (posterior) displaced and/or positioned condyles due to macro or micro trauma (orthodontic procedures or the lack of attention to condyle position) would cause TMJ internal derangements.²⁹ The most noteworthy finding was thought to be anterior-medial displacement of the TMJ disks. The thinking behind the allegations in the Brimm case—that TMJ internal derangements could be caused by distal (posterior) forces (dental procedures or trauma) applied to the mandibular condyles—dates back to the notion of Farrar and McCarty.^30,31 Subsequent to Brimm, Anthony Gianelly, DMD, PhD, MD, and his colleagues from Boston University performed a number of studies that totally disproved the allegations in the case. That is, there is no difference in the condyle position (they were not distally displaced) of orthodontic patients whether they have had extractions, no extractions, had extractions in the upper arch only and/or the upper and lower arch, or whether a nonorthodontic group possessed an Angle’s Class II (2) deep-bite, no-overjet malocclusion.^32-36

Donald J. Rinchuse, DMD, MS, MDS, PhD, is a clinical professor of orthodontics at the University of Pittsburgh School of Dental Medicine and is also in private practice in Greensburg, Pa. He is a Diplomate of the American Board of Orthodontics and has published extensively with many of his articles dealing with the topic of occlusion/TMJ. He has been involved in orthodontic education, research, and clinical practice for more than 30 years. He can be reached at

Sanjivan Kandasamy, BDSc, BScDent, DocClinDen, MOrthRCS, is a research associate in orthodontics at the School of Dentistry at the University of Western Australia, and is in private practice in Perth, Australia.

Daniel Rinchuse, DMD, MS, MDS, PhD, is a clinical professor of orthodontics and dentofacial orthopedics at the University of Pittsburgh School of Medicine.

References

1. Rinchuse DJ, Kandasamy S. Articulators in orthodontics: An evidence-based perspective. Am J Orthod Dentofacial Orthop. 2006;129:299-308.
2. Rinchuse DJ, Kandasamy S. Centric relation: A historical and contemporary orthodontic perspective. J Am Dent Assoc. 2006;137:494-501.
3. Rinchuse DJ. Counterpoint: A three-dimensional comparison of condylar position changes between centric relation and centric occlusion using the mandibular position indicator. Am J Orthod Dentofacial Orthop. 1995;107(3):319-328.
4. Rinchuse DJ, Rinchuse DJ, Kandasamy S. Evidence-based versus experience-based views on occlusion and TMD. Am J Orthod Dentofacial Orthop. 2005;127:249-254.
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6. Rinchuse DJ, McMinn JT. Summary of evidence-based systematic reviews of canine protected occlusion. Am J Orthod Dentofacial Orthop. 2006;130:715-720.
7. Rinchuse DJ. Counterpoint: Preventing adverse effects on the TMJ through orthodontic treatment. Am J Orthod Dentofacial Orthop. 1987;91(6):500-506.
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